A Spanish doctor named Michael Servetus was burned alive in Geneva on 27 October 1553. He was a brilliant man: he was among the first Europeans to describe how blood passes through the lungs. His crime was a book arguing against the doctrine of the Trinity. Catholic and Protestant authorities had both condemned him.
This is an argument inside Christianity. It is Christianity's own story, and we tell it carefully, because it is sometimes picked up in conversations between Muslims and Christians and bent out of shape. The honest version is more interesting: a long, sometimes painful debate about how to speak of the One God, carried on by people who all read the same Bible.
“Jesus answered, “The greatest is, ‘Hear, Israel, the Lord our God, the Lord is one:”
Mark 12:29 · WEB
Asked which commandment comes first, Jesus (peace be upon him) quoted the Shema of Deuteronomy 6:4. Every Christian group on this page, Trinitarian or not, starts from this verse. The same Gospels also close with Jesus sending his followers to baptise 'in the name of the Father and of the Son and of the Holy Spirit' (Matthew 28:19). How those two verses belong together is the question this history keeps returning to.
What history shows
The mainstream first. Most Christians, Catholic, Orthodox and Protestant, confess one God in three persons. The Catechism of the Catholic Church says: 'We do not confess three Gods, but one God in three persons.' The creed agreed at Nicaea in 325 and expanded at Constantinople in 381 describes the Son as 'of one substance with the Father'. Historians stress that Nicaea did not invent belief in Father, Son and Spirit, which Christians already used in baptism and worship. It defined the words for it.
The Ebionites (roughly the first to the fifth centuries) were Jewish followers of Jesus, living mainly east of the Jordan and in Syria. They kept the Torah, and they saw Jesus as a righteous man chosen by God at his baptism, not as a divine person. Most, perhaps all, of them rejected the virgin birth. Almost everything we know about them comes from the church writers who opposed them, such as Irenaeus (around 180) and Epiphanius (around 375), so historians read the evidence with care. Whether they were the same group as the 'Nazarenes' is still debated.
Arius (about 256–336) was a priest in Alexandria. He taught that the Son was divine and the one through whom God made the world, but that the Son was himself created: 'there was when he was not'. The Council of Nicaea rejected this, yet the argument ran on for some sixty years. Through the missionary Ulfilas, who translated the Bible into Gothic, a form of Arian Christianity spread among the Goths, Vandals and Lombards and lasted into the seventh century. Note that Arius did not think of Jesus as only a man; he gave the Son a very high place.
Modern scholars, including Rowan Williams in his book Arius (1987) and R. P. C. Hanson (1988), add a caution: 'Arianism' as a single movement is partly the creation of its opponents, above all Athanasius. The people grouped under that label disagreed among themselves.
After the Reformation the question returned. In Transylvania, the Edict of Torda (1568) let preachers teach according to their understanding, and it is often called one of Europe's first laws of religious toleration. There a Unitarian church grew up whose motto is Egy az Isten, 'God is one'. Its leader, Ferenc Dávid, died in prison in 1579, but the church survives: Romania's 2002 census counted 66,846 Unitarians, and the church itself estimates more.
In England, John Biddle (1615–1662) wrote against the Trinity and died in prison. Isaac Newton held similar views in private notebooks and never published them. On 17 April 1774 Theophilus Lindsey, who had given up his post as a Church of England minister, opened Essex Street Chapel in London, the first openly Unitarian congregation in England. Today the General Assembly of Unitarian and Free Christian Churches has about 170 congregations, and many of its members no longer describe themselves as Christian.
Two cautions. First, these groups were never the majority, and they differ a great deal from one another, so there was no single 'original' non-Trinitarian church waiting to be rediscovered. Second, the line 'the real Christians were unitarian' is not supported by historians. Later movements, such as the Christadelphians (1848) and Jehovah's Witnesses (from the 1870s), describe their own beliefs in their own ways, and should be heard in their own words.
What each faith says
Judaism
“HEAR, O ISRAEL: THE LORD OUR GOD, THE LORD IS ONE.”
Deuteronomy 6:4 · JPS 1917
This is not Judaism's argument, but Judaism's prayer stands at the centre of it. Twice a day Jews say the Shema, and many say it again at bedtime. Jewish thinkers such as Saadia Gaon and Maimonides taught that God's oneness is unlike any other kind of oneness and has no parts. Maimonides put God's unity second in his Thirteen Principles of faith, which many Jews sing each Friday night in the hymn Yigdal.
Over the centuries rabbis also debated how to regard their Christian neighbours. Many, especially in medieval Europe, concluded that Christians worship the Creator of heaven and earth, understood in their own way. That debate is Judaism's own, and it continues: Orthodox, Reform, Liberal and Masorti rabbis in Britain still answer it in different tones.
Christianity
“The grace of the Lord Jesus Christ, God’s love, and the fellowship of the Holy Spirit, be with you all. Amen.”
2 Corinthians 13:14 · WEB
For the great majority of Christians, the Trinity is not a puzzle added to faith but the heart of it. The Catholic Catechism calls it 'the central mystery of Christian faith and life' (CCC 234). Christians say that God has shown Himself as Father, Son and Holy Spirit, and that this is how they meet Him in prayer: to the Father, through the Son, in the Spirit. The Church of England's first article of religion says 'there is but one living and true God', and in the same breath, 'in unity of this Godhead there be three Persons'.
Christians also insist that the Trinity is monotheism, not three gods. They read the Shema and the baptism command together. The groups on this page read the same verses and reached different answers. Churches have judged those answers to be wrong, and in the past they sometimes punished them cruelly. Many Christians today look back on burnings like Servetus's with shame, while still holding the creed he rejected.
Islam
“The Messiah, Jesus son of Mary, was only a messenger of Allah, and His word which He conveyed unto Mary, and a spirit from Him. So believe in Allah and His messengers, and say not "Three" - Cease! (it is) better for you!”
Qur'an 4:171 · Pickthall (1930)
Islam's own position is plain: God is one, and Jesus (peace be upon him) is a mighty messenger and the Messiah, born of Mary (peace be upon her), not divine. The Qur'an addresses Christians directly on this point and asks them not to say 'Three'. It also speaks warmly of Christians: of priests and monks who are not proud (5:82), and of people of the Book who stand in prayer at night reciting God's verses (3:113).
Muslims sometimes point to the groups on this page as evidence for their own view of Jesus. Fairness asks for care. The Ebionites, Arius and the Unitarians each had their own beliefs, which are not Islam's, and the mainstream churches have always been Trinitarian. The Qur'an's instruction is to argue only 'with what is best' (29:46), which means describing others as they describe themselves.
Same and different
Jews, Christians and Muslims all confess that God is one, and all three treasure the Shema or its echo. Here they genuinely differ: most Christians understand the one God as Father, Son and Holy Spirit; Jews and Muslims do not. Judaism teaches that God's oneness admits no division of any kind. Each is distinctive elsewhere too. Judaism lives its oneness through a covenant of commandments rather than creeds. Islam honours Jesus as Messiah and prophet but not as divine, a position neither Jews nor Christians hold. The minority Christian groups on this page do not erase those differences. They show that Christians themselves have argued long and hard about how to speak of God, and that the creeds most Christians say today were shaped in that argument.
A moment to reflect
- Have you and someone close to you read the same words and understood them differently? What happened?
- How should a community treat people inside it who come to disagree on something central?
- When you hear history used to win an argument, how can you check whether it has been told fairly?
- What is the difference between saying 'I believe you are wrong' and 'you do not belong here'?
Watch
A clear, gentle explanation of the Trinity from a widely used Christian Bible channel: the mainstream view in its own words.
An Oxford historian of the early church on how the doctrine of the Trinity developed.
A balanced history of Arius and the Council of Nicaea, including what Arius actually taught.
The Transylvanian Unitarians tell their own history.
Do it together
Print the Shema (Deuteronomy 6:4), the opening of the Nicene Creed and Sura al-Ikhlas (Qur'an 112) side by side. Ask a member of each faith to read their own text aloud and say in a sentence what it means to them. Listen first; discuss after.
Give groups one claim each, such as 'the Trinity was invented at Nicaea' or 'the first Christians were unitarian'. They check it against this page and its sources and report back: true, false or more complicated, and why.
Many historic chapels, including Unitarian ones, open their doors for Heritage Open Days each September. Visit one, and a parish church nearby, and compare what each building tells you about what its people believed.
Yigdal, a hymn sung in many synagogues on Friday night, turns Maimonides' Thirteen Principles into verse, including God's oneness. Listen to a recording and read an English version, then talk about the difference between a creed you say and a creed you sing.
Go deeper
- Catechism of the Catholic Church, the Holy Trinity (paragraphs 232–267) · article
- Ebionites (Wikipedia) · encyclopaedia
- Arianism (Encyclopaedia Britannica) · encyclopaedia
- Unitarian Church of Transylvania (Wikipedia) · encyclopaedia
- Mark 12 (World English Bible) · scripture
- Qur'an 4:171 · scripture
- Deuteronomy 6, the Shema (Sefaria) · scripture
- Mishneh Torah, Foundations of the Torah 1:7, on God's oneness (Sefaria) · scripture
Sources (8)
- 'We do not confess three Gods, but one God in three persons' (CCC 253); 'the central mystery of Christian faith and life' (CCC 234): Catechism of the Catholic Church
- Ebionites: Jewish followers of Jesus, Torah-observant, Jesus a righteous man chosen at baptism; known mainly from Irenaeus and Epiphanius; Nazarene link debated: Wikipedia, Ebionites (summarising standard scholarship)
- Arius: the Son divine and creator but created, 'there was when he was not'; Nicaea 325; Gothic Arianism through Ulfilas: Encyclopaedia Britannica, Arianism
- 'Arianism' as one movement largely a construct of Athanasius's polemic: Rowan Williams, Arius: Heresy and Tradition (1987); R. P. C. Hanson, The Search for the Christian Doctrine of God (1988)
- Edict of Torda 1568; Ferenc Dávid died in prison 1579; 66,846 Unitarians in Romania's 2002 census: Wikipedia, Unitarian Church of Transylvania (citing the census)
- Servetus burned in Geneva, 27 October 1553; described pulmonary circulation: Encyclopaedia Britannica, Michael Servetus
- Theophilus Lindsey opened Essex Street Chapel, 17 April 1774, the first openly Unitarian congregation in England: Encyclopaedia Britannica, Theophilus Lindsey
- General Assembly of Unitarian and Free Christian Churches: about 170 congregations: Unitarians UK